1. Field of the Invention
The present invention relates to alumina sintered bodies and base substrates for optical devices.
2. Description of the Related Art
Transparent alumina sintered bodies have been known. For example, in NPL 1, an alumina suspension containing MgO is subjected to slip casting under a magnetic field and fired in a vacuum at 1850° C. for 5 hours to produce a transparent alumina sintered body with oriented grains. For example, an alumina sintered body produced under a magnetic field of 12 tesla has an in-line transmittance at 600 nm of 70.3% and a high degree of orientation of 97%. An alumina sintered body produced under a magnetic field of 8 tesla has an in-line transmittance at 600 nm of about 56% and a slightly high degree of orientation of 78%. Furthermore, the in-line transmittance and the degree of orientation decrease as the magnetic field strength decreases to 6 tesla and 4 tesla. The results conclude that the in-line transmittance and the degree of orientation increase as the magnetic field strength increases.